Method of making orthopaedic implant by welding

ABSTRACT

A method of forming an orthopaedic implant having a porous surface, the method including the steps of providing a porous surface including a porous layer attached to a substantially solid layer; positioning the porous layer on the orthopaedic implant; providing a high energy density welding device capable of producing a high energy density weld beam; and forming a weld bead substantially about the periphery of the porous layer by directing the high energy density weld beam about the periphery of the porous layer, wherein the weld bead bonds the porous layer to the implant. Two shaped porous pads may also be welded together about an implant body to avoid welding the body itself.

This is a division of application Ser. No. 08/228,774 filed Apr. 18,1994 now U.S. Pat. No. 5,504,300.

FIELD OF THE INVENTION

This invention relates to orthopaedic implants having a porous outerlayer and has specific relevance to an implant having a porous layerattached to the implant body by welding.

BACKGROUND OF THE INVENTION

It is known to have a portion of an orthopaedic implant covered by aporous layer to promote the ingrowth of bone within the openings of theporous layer for long term fixation of the implant to the bone.Diffusion bonding is the most widely known and accepted method ofattaching the porous layer to the implant. Diffusion bonding a porouslayer to a substrate on a curved surface, such as a portion of a hipstem, is a time-consuming and expensive task. Further, diffusion bondinga porous material to a substrate can cause notches to be formed in thesubstrate, thereby decreasing the strength of the substrate. Tocompensate for this effect, orthopaedic implant manufactures may eitherlimit the amount of the porous layer attached to the substrate or adjustthe size of the substrate to increase its strength.

SUMMARY OF THE INVENTION

The method and implant of this invention provide for the attachment of aporous pad to the implant by laser welding. The porous pad is comprisedof a flat sheet of porous material that is diffusion bonded to a thinmetal foil layer. Diffusion bonding between the flat foil to the porousmaterial is substantially less troublesome than when bonding on a curvedsurface. After the metal foil is bonded to the porous material to form aporous pad, the pad is cut to the desired shape to form a blank. Theblank is stamped into a shape substantially conforming to its intendedlocation on the implant. The blank is positioned on the implant andlaser welded to the substrate. If the porous surface is intended tosurround a portion of the implant such as would be seem on a porous hipstem, a second blank is cut and stamped. The two stamped blanks arepositioned about the implant such that they abut at their edges. Theblanks are then welded together using a laser welder to form an integralporous layer about the implant. The porous pads may also be welded usingthe laser welder to the implant at their ends to seal the interface ofthe porous pad and implant. By first bonding the porous material to thinfoil to form the pad and then connecting the blanks cut and stamped fromthe blanks to the implant by laser welding the formation of notches inthe implant body is eliminated. The laser beam is controlled such thatthe substrate is not affected by the welding process. Therefore, byconnecting the porous layer in this manner, the implant manufacturer isnot limited as to the amount of porous surface that can be connected tothe implant body. Further, laser welding a porous pad to the substrateis a quicker and less expensive method of attaching as compared to thediffusion bonding process.

In an alternative embodiment, a polymer layer could be positionedbetween the pad and substrate. The polymer layer would adhesively bondthe pad and substrate together to eliminate the need for unique wiltingclamps and also would assist in transferring stress to the substrate ina more uniform manner. The polymer would also assist in filling gapsbetween the pad and the substrate thereby allowing the manufacturer toreduce the manufacturing tolerances for the substrate and pad.

In a further variation of the invention, the thin metal foil may includesmall holes to allow the ingress and egress of fluid from the spacebetween the pad and substrate.

The terms laser weld, laser welder or laser beam are used throughoutthis application to refer to any high energy density welding processsuch as laser or electron beam welding.

Accordingly, it is an advantage of this invention to provide for a novelorthopaedic implant having a porous surface layer connected to theimplant body by welding.

Another advantage of the invention is to provide for a novel method ofattaching a porous surface to an orthopaedic implant.

Yet another advantage of the invention is to provide a method ofattaching a porous surface to an implant without detrimentally effectingthe strength of the implant.

Another advantage of the invention is to provide an orthopaedic implantwherein the interface between the porous surface layer and the implantbody is sealed.

Other advantages of this invention will become apparent upon a readingof the following description taken with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a substantially flat porous blank for ahip stem implant which has been cut from a larger porous pad.

FIG. 2 is a perspective view illustrating the stamping process used toform the flat porous blank of FIG. 1 into the shape to fit a portion ofa hip stem implant.

FIG. 3 is an exploded perspective view of a hip stem configured foraccepting the shaped blanks of FIG. 2.

FIG. 4 is a perspective view of the hip stem and blanks of FIG. 3 afterthe welding process is complete.

FIG. 5 is a cross-sectional view taken along lines 5--5 of FIG. 4.

FIG. 6 is an elevational view of a substantially flat blank formed in analternative manner such that the metal foil extends beyond the porousmaterial.

FIG. 7 is a side elevational view of FIG. 6.

FIGS. 8 and 9 illustrate the shaping of the substantially flat blank ofFIGS. 6 and 7 with a stamping die such that the foil extends along theside edges of the porous material.

FIG. 10 is an elevational view illustrating the porous pad of FIGS. 6through 10 positioned within a recess of a tibial plate.

FIG. 11 is a cross sectional view taken along lines 11--11 of FIG. 10and prior to welding.

FIG. 12 illustrates the cross-sectional view of FIG. 11 after the porouspad has been laser welded to the implant.

FIG. 12A illustrates an alternative method wherein the pad of FIG. 7 isplaced into the recess and welded thereto without bending the extendingedges upwardly.

FIG. 13 is a diagram illustrating the method of laser welding the porouspads to an implant. The implant and porous pads are illustrated incross-section.

FIG. 14 is an enlarged cross sectional view of the area circled in FIG.10 and identified by number 14.

FIG. 14A is a diagram illustrating the method of laser welding theporous pads within the recess of an implant (only partially shown).

FIG. 14B is the enlarged cross sectional view of FIG. 14 after theporous pad has been welded to the implant.

FIG. 15 is a diagram illustrating a method for laser cladding the porouspads to the implant.

FIG. 15A is an enlarged cross sectional view illustrating the claddedjunction between the porous pad and the implant.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments herein described are not intended to beexhaustive or to limit the invention to the precise forms disclosed.Rather, they are chosen and described to best explain the invention sothat others skilled in the art might utilize their teachings.

The methods of the invention are illustrated in the figures to yield animplant having a porous structure welded to the body of the implant. Themethod begins with the formation of a porous pad 10 having a poroussurface 12 and a thin metal backing 14. Preferably, a large sheet of theporous material, such as fiber metal, is diffusion bonded to a similarlysized thin metal sheet or foil. After the diffusion bonding process,blanks 8 are cut from the sheet using laser cutting or a device whichcan cut through the pad without substantially deforming the edges of theblank. Blanks 8 are then placed within a stamping die 16 havingcooperating male and female sections as illustrated in FIG. 2. Stampingdie 16 includes cooperating male and female parts which come togetherunder force and forms the blanks 8 into pads 10 which substantiallyconform to a portion of hip implant 17 as shown in FIG. 3. In thepreferred embodiment, implant 17 includes a stem portion 16 whichincludes a reduced section forming shoulders 18 and 20. The reducedsection is provided to accommodate the blanks. Shoulders 18 and 20 areprovided to abut the distal and proximal ends of the blanks and assistin preventing the shaped pads 10 from shifting longitudinally relativeto the implant 17. Once the blanks 8 are formed into shaped pads 10, thepads are placed onto the implant and temporarily held in place by aclamp device (not shown). Alternatively, a quantity of an adhesivepolymer could be placed between the pads and stem to hold the pads inplace during welding. The polymer would also assist in transferring theload to the stem in use. Once clamped to the implant, a laser is guidedalong the seams between the pads 10 forming a weld bead 22 to cause aportion of the pads to melt together thereby forming an integral padabout the body of the implant. As known in the welding industry, theintensity of the laser may be controlled to precisely control the depthof the weld bead. In the preferred embodiment, the intensity of the weldbead is set such that the bead is formed only between the porous padsand does not invade the outer surface of the implant. Once welded, theporous pads are securely held between the shoulders 18, 20 of theimplant. To assist in the mechanical fixation of the stem the laserwelder may be guided around the proximal and distal shoulder of theimplant to weld the pad to the shoulder of the implant. Therefore, theinterface between the pad and the implant is sealed by the laser weld.The sealing of the interface between the pad and the implant wouldprevent the ingress of the body fluids.

An alternative method is illustrated in FIGS. 6 through 12. In themethod of FIGS. 6-12, the porous material 30, preferably fiber metal, iscut to shape and then diffusion bonded to a thin metal foil 32 having asimilar shape. The metal foil is slightly larger than the porousmaterial and extends outwardly therefrom as illustrated. The fiber metal30 and foil 32 are diffusion bonded in a known manner and are thenplaced into a stamping die 34 and stamped such that the portion of thefoil extending outwardly from the fiber metal is bent around the sideedges of the fiber metal as illustrated in FIGS. 8 and 9 to form a fibermetal pad 36 a foil bottom portion and side portions. The fiber metalpad 36 is placed within a matching recess 38 of an implant. In FIGS. 10through 12, the fiber metal pad 30 is shown positioned within a matchingrecess 38 on the bone engaging surface of a tibial knee component 40(partially illustrated). As illustrated, the fiber metal pad standsproud relative to the implant with the foil extending slightly above theimplant surface. The small amount of foil extending above the implantprovides the material which forms the weld bead 42 during the weldingprocess. After positioning in the matching recess, the pad is laserwelded to the implant at the junction between the implant and the foilalong the edge of the pad. FIG. 12 illustrates the pad 36 after weldingto the implant. The weld may be directed completely around the peripheryof the fiber metal pad thereby sealing the area between the pad and theimplant from the ingress of moisture. Further, the pad may be formedwith openings to accommodate screw holes or fixation posts as are wellknown in the industry. Using the laser welding technique of theinvention, the pad may be welded about such openings to enhance fixationof the pad to the implant.

In a preferred variation of the above method the stamping process iseliminated. Therefore, as illustrated in FIG. 12A, the foil 32' extendsbeyond the fiber metal layer 30' a predetermined amount but is shaped soas to closely approximate the cavity 38 formed in the implant 40. Thelaser beam is directed along the extending portion of the foil to securethe foil to the implant along the weld bead as illustrated in FIG. 12A.

FIG. 13 illustrates in diagram form the laser welding of the hip stem ofFIGS. 1 through 5. The particular type of laser welder used is one ofchoice to the manufacturer and are commercially available. Given thatlaser welding in general is known, it will not be discussed here. Whatis important is that the power or intensity of the laser can becontrolled such that the laser beam only affects the fiber metal padlocally and does not extend into implant substrate. Laser weldingradiates less heat to the body of the implant than other weldingtechniques such as plasma or arc welding. Therefore the use of the laseris the preferred method to ensure that the metallurgy of the implant isnot detrimentally changed by the welding process.

FIGS. 14 and 14A illustrate in diagram form the laser welding of thefiber metal pad of FIGS. 6 through 12. Here, since the welding processis joining the metal foil to the implant, some deformation of theimplant is necessary to effect the weld. However, by use of the laserwelder 50, the extent of the deformation will be localized along theweld bead, thereby preventing detrimental metallurgical changes in theimplant body. As illustrated, a portion of the foil 32 extends above theimplant surface and forms the material used in the welding process toform the weld bead 42. FIG. 14B illustrates the section of 14A after thewelding process is completed.

FIG. 15 illustrates in diagram form laser cladding as an acceptablealternative to laser welding a fiber metal pad to an implant body. As iswell known, laser cladding calls for the injection of metal powder 60into the path of the laser beam 62. The laser beam 62 melts the powderand deposits the melted metal precisely on the implant. In theapplication of the current invention, the cladding process may be usedin association with the embodiment of FIGS. 6 through 12 to fill in thespace between the sides of the fiber metal pad and the implant. As thecladding process occurs, the molten metal deposited bonds the implant tothe fiber metal pad at a point of contact and forms a fillet 64 ofmaterial as shown in FIG. 15A. Cladding could be a particular advantagein the process as the tolerances of the implant recess and the fibermetal pad could be reduced with any gap being filled in by the claddingprocess.

It should be understood that the cladding process utilized in keepingwith the method of this invention could also be wire feed cladding orsimilar know processes for welding.

It should also be understood that the invention should not be limited tothe precise details above but may be modified within the keeping of theappended claims.

We claim:
 1. A method of forming an orthopaedic hip stem prosthesishaving an annular porous surface, the method comprising the steps of;a)providing an orthopaedic hip stem implant having a body including anelongated stem portion and a neck portion; b) providing a first porouspad having a solid surface and a porous surface and including terminaledges; c) forming the first porous pad to substantially conform to aportion of the implant body and stem; d) providing a second porous padhaving a solid surface and a porous surface and including terminaledges; e) forming the second porous pad to substantially conform to aportion of the implant body and stem; f) positioning the first porouspad and the second porous pad about the implant such that terminal edgesof the first and second porous pads are adjacent; and g) forming a weldbead along the terminal edges to weld the first porous pad to the secondporous pad such that the weld bead does not contact the body of theimplant.
 2. The method of claim 1, wherein the implant includes at leastone annular shoulder, a refund edge of the first and second porous padlying adjacent the shoulder.
 3. The method of claim 2 including the stepof welding the second mentioned edge of the first and second porous padto the shoulder of the implant.